Stroke, also known as cerebrovascular accident (CVA), is one of the leading causes of mortality and morbidity with an estimated 700,000 patients diagnosed with stroke each year. Stroke currently ranks third in the cause of death in the U.S.A.
The term “stroke” encompasses two widely different clinical settings which it is of the utmost importance to distinguish. Ischemic stroke is thus usually caused by the blockage of blood vessels and is best treated by clot dissolving agents, such as t-PA, within three hours of symptom onset. In contrast, hemorrhagic stroke is caused by bleeding into the brain which forbids any treatment by anti-clotting agents, which could prove fatal.
Transient ischemic attack (TIA, often colloquially referred to as “mini stroke”) is caused by the changes in the blood supply to a particular area of the brain, resulting in brief neurologic dysfunction that persists, by definition, for less than 24 hours; if symptoms persist then it is categorized as a stroke (see e.g. Transient Ischemic Attacks: Stroke (CVA): Merck Manual Home Edition). Patients diagnosed with a TIA are sometimes said to have had a warning for an approaching stroke. If the time period of blood supply impairment lasts more than a few minutes, the nerve cells of that area of the brain die and cause permanent neurologic deficit. One third of the people with TIA later have recurrent TIAs and one third have a stroke due to permanent nerve cell loss (Transient ischemic attack Mount Sinai Hospital, New York). Therefore, the identification of TIA is beneficial because these patients are at increased risk of future stroke.
The diagnosis of stroke, and the segmentation between ischemic and hemorrhagic stroke, in patients which present with symptoms indicative of stroke, such as sudden numbness or blindness, confusion, severe headaches, slurred speech, and partial paralysis, currently essentially relies on computed tomography (CT). CT, however, is not completely satisfying since it has an estimated sensitivity of less than 26% in diagnosing acute stroke (Chalela et al. (2007) Lancet 369:293-298), which is linked to a very poor performance in detecting ischemic stroke, with less than 33% sensitivity (Reynolds et al. (2003) Clin. Chem. 49:1733-1739). Magnetic resonance imaging (MRI) has been shown to be superior to CT in diagnosing acute stroke (84% sensitivity, Chalela et al. (2007) Lancet 369:293-298), and particularly ischemic stroke. However MRI scanners are costly equipments and are not always available in the emergency room.
Accordingly there is still the need for alternative or complementary methods, in particular to CT, for diagnosing stroke and TIA.
In this respect, biochemical markers have been suggested as an aid in detecting stroke, in particular in view of the early detection of ischemic stroke.
S-100b (a marker of astrocytic activation) and neuron-specific enolase (NSE) are among the best characterized such markers (Jauch et al. (2006) Stroke 37:2508-2513). Heart-type fatty acid binding protein(H-FABP) has also been considered as a promising marker (Lescuyer et al. (2005) Mol. Diagn. 9:1-7). However, it seems that the discriminatory power offered by these markers individually is not sufficient to be of clinical value.
It has thus been suggested to use panels combining several markers, such as S-100b, the B-type neurotrophic growth factor (BNGF), the von Willebrand factor (vWF), matrix metalloproteinase-9 (MMP-9) and monocyte chemotactic protein-1 (MCP-1), for diagnosing ischemic stroke (Reynolds et al. (2003) Clin. Chem. 49:1733-1739). Indeed, this panel was shown to provide a sensitivity of 92% at 93% specificity for ischemic stroke sample within 6 hours from symptom onset. Within 3 hours from onset however, sensitivity is of only 87%, which might be due to a too low individual sensitivity/specificity of the markers.
Accordingly, there is still the need for alternative markers offering a good individual sensitivity/specificity ratio to be used in single-marker tests or to improve multi-marker panels, either by increasing sensitivity/specificity or by enabling reducing the number of markers which levels have to be measured in panels.
proBNP(1-108), a precursor protein of 108 amino acids, is cleaved in vivo to yield (i) Brain Natriuretic Peptide (also referred to as BNP(32) or simply BNP), which consists of the 32 C-terminal amino acids of proBNP(1-108) and (ii) NT-proBNP(1-76), which consists of the 76 N-terminal amino acids of proBNP(1-108) (Giuliani et al. (2006) Clinical Chemistry 52:1054-61). Biologically, BNP is a blood pressure regulatory agent which is released mainly from the left cardiac ventricle in response to volume expansion and pressure overload. proBNP(1-108) has been shown to be circulating in patients with severe heart failure (Hammerer-Lercher et al. (2008) Clinical Chemistry 54:5).